1. Field of the Invention
The present invention relates to an optical probe.
2. Description of Related Art
Non-contact optical probes have conventionally been known (see Japanese Translation Publication of PCT International Application No. 2009-534969, for example). Such non-contact optical probes irradiate an object to be measured (hereinafter referred to as a work) with laser light, detect light reflected from the surface of the work, and obtain position coordinates of the respective spots of the work.
As an example of the non-contact optical probes, a linear optical probe 100 as shown in FIG. 10 has been known. The linear optical probe 100 uses a beam expander 103 that allows laser light to change shape into light L1 that is linear in shape (hereinafter referred to as linear laser light). In the linear optical probe 100, laser light emitted from a laser light source 101 is converted into parallel light with a collimator lens 102. Then, the beam expander 103 allows the parallel light to change shape into linear laser light L1. Thus, a work W is irradiated with the linear laser light L1. The linear laser light L1 thrown to the work W is reflected on the surface of the work W to be incident upon an image pickup element (not shown). In this way, the linear optical probe 100 can measure the form of the work W “at one time”.
As another example of the non-contact optical probes, a flying spot optical probe 200 as shown in FIG. 11 has been known. The flying spot optical probe 200 uses a rotary galvanometer mirror 203. In the flying spot optical probe 200, laser light emitted from a laser light source 201 is incident upon the galvanometer mirror 203 through a mirror 202. Then, discrete points of light L2 (hereinafter referred to as point laser light) reflected from the galvanometer mirror 203 irradiate a work W. The galvanometer mirror 203 is driven to rotate with respect to the incident light. The point laser light L2 scans the surface of the work W in such a way that the point laser light L2 draws a line in accordance with the rotary drive of the galvanometer mirror 203. The point laser light L2 which has scanned the surface of the work W is reflected thereon to be incident upon an image pickup element (not shown). In this way, the flying spot optical probe 200 can measure the form of the work W “in sequence”.
As still another example of the non-contact optical probes, a rotating mirror optical probe 300 as shown in FIG. 12 has been known. The rotating mirror optical probe 300 uses a rotary polygon mirror 303. In the rotating mirror optical probe 300, laser light emitted from a laser light source 301 is incident upon the polygon mirror 303 through a mirror 302. Then, discrete points of light L3 (hereinafter referred to as point laser light) reflected from the polygon mirror 303 irradiate a work W. The polygon mirror 303 is driven to rotate with respect to the incident light. The point laser light L3 scans the surface of the work W in such a way that the point laser light L3 draws a line in accordance with the rotary drive of the polygon mirror 303. The point laser light L3 which has scanned the surface of the work W is reflected thereon to be incident upon an image pickup element (not shown). In this way, the rotating mirror optical probe 300 can measure the form of the work W “in sequence”, similarly to the flying spot optical probe 200.
In general, a light-section method is used for non-contact optical probes, as a measurement principle. For example, as shown in FIG. 13 and FIG. 14, when the linear optical probe 100 measures the form of a work W in the light-section method, the surface of the work W is irradiated with the linear laser light L1 from the laser light source 101 through an optical system (a collimator lens and a beam expander, which are not shown). Therefore, it is only necessary to pick up an image of the area, which is irradiated with the laser light, by an image pickup element 104 to measure the form of the work W. The linear optical probe 100, which does not have a moving mechanism in the optical system, is easier to maintain compared with the flying spot optical probe 200 and the rotating mirror optical probe 300.
When a work having a mirror plane or a corner, in particular, is irradiated with laser light from a conventional optical probe, a false shape (virtual image) is sometimes obtained due to multiple reflections.
In the case of the linear optical probe 100, as shown in FIG. 15 and FIG. 16, laser light is constantly thrown in a linear shape, and the form of the work W is obtained at one time. Accordingly, when a virtual image is formed due to multiple reflections, a real image R and a virtual image V cannot be distinguished from each other, which is inconvenient.
In this regard, the flying spot optical probe 200 and the rotating mirror optical probe 300 irradiate a work W in such a way that the point laser light draws a line thereon to obtain the form of the work W in sequence. Accordingly, the flying spot optical probe 200 and the rotating mirror optical probe 300 can relatively easily recognize a virtual image formed due to multiple reflections.
The flying spot optical probe 200 and the rotating mirror optical probe 300, however, are more complex in structure compared with the linear optical probe 100 because each of the probes 200 and 300 needs a moving mechanism in the optical system thereof as described above. Accordingly, maintenance of the probes 200 and 300 is troublesome.
Further, in the case of the flying spot optical probe 200, which needs to control an operating angle of the galvanometer mirror 203 with a motor or the like, the form of a work W cannot be accurately measured unless the operating angle of the galvanometer mirror 203 is controlled precisely. Still further, since the galvanometer mirror 203 is a moving mechanism, it is subject to performance deterioration after a long period of use. Therefore, it is essential to maintain the galvanometer mirror 203.
Furthermore, in the case of the rotating mirror optical probe 300, it is necessary to improve the profile accuracy (flatness, in particular) of the polygon mirror 303 as much as possible to take an accurate measurement of the form of a work W. That is because the measurement accuracy depends on the profile accuracy of the polygon mirror 303. Since the polygon mirror 303 is mirrors of a polyhedron, the form of a work W cannot be accurately measured unless the faces of the polygon mirror 303 have uniform surface accuracy.